This invention relates generally to the field of printing machines such as office typewriters, teleprinters, data printers and the like which utilize a ribbon for imprinting characters, and more particularly to an improved mechanism for advancing the ribbon after each character print-out.
For the satisfactory operation of printing machines which utilize a ribbon for effecting character print-out, it is desirable that the ribbon should be advanced by a predetermined amount after each individual character print-out. When ribbons of finite length are used, it is also necessary, in the economical use of such ribbons, to reverse the direction of movement of the ribbon after each full printing cycle, in order to automatically produce a number of ribbon cycles. Methods of and means for obtaining such reversal from switching criteria such as, for example, ribbon tension, have been heretofore known.
In printing devices in which the paper carriage is stationary in the direction of the printed row of characters and the type carrier carriage is moved along the row, it is known to arrange the ribbon supply and feeding mechanism on the moving type carrier carriage. The drive movement for the ribbon can be transferred to the moving type carrier carriage by a motor similarly arranged on the type carrier carriage or by drive means which are located in the stationary part of the machine, via gear elements. Drive motors arranged on the moving type carrier carriage load the latter to a considerable extent due to an increased moment of inertia and thus impede the high acceleration and speed of movement which is required, particularly in respect of the return movement of the carriage to the starting position at the beginning of the next row of characters to be printed.
If the drive motion for the ribbon is transferred to the movable type carrier carriage from a drive mechanism located on the stationary part of the printing machine through various gear elements it is desirable for the drive connection to be maintained only during the printing operation as the type carrier carriage moves in one direction, but not as the carriage is being returned to the beginning of the next row. While there exist various mechanisms for performing this function, such mechanisms are generally quite expensive.
On the other hand, arrangements have been previously disclosed whereby the movement for the ribbon is derived from the printing movement of the type carrier carriage, but in such situations the non-uniform loading by the ribbon drive can often impair the quality of printing.
An object of the present invention is to provide apparatus for advancing a ribbon whose supply mechanism is located on a type carrier carriage which moves along the printing row, which apparatus produces an acceptable load level on the type carrier carriage, and can be selectively operated by drive means disposed on the stationary part of the printing machine.
Apparatus satisfying these objects and constructed in accordance with the principles of the present invention may be characterized as comprising a cable mounted on the stationary part of the printing machine and looped around a drive roller connected for joint rotation to a ribbon reel mounted on the movable type carrier carriage. The cable may be selectively tensioned and relaxed to either rotate the ribbon reel as the type carrier carriage moves in relation to the stationary part of the printing machine, or to be ineffective with respect to the ribbon reel. In printing machines in which the direction of movement of the ribbon is reversed to accommodate plural ribbon printing cycles, two ribbon reels may be utilized, each having a corresponding drive roller about which the cable is looped.
Thus, for example, in accordance with the principles of the present invention, in printing machines in which the type carrier carriage moves relative to the paper carriage along the row of printed characters, the drive roller around which the cable is looped moves with the type carrier carriage. If the cable is relaxed, then slippage occurs between the cable and the drive roller, and the ribbon reel is therefore not drivingly connected to the cable. On the other hand, when the cable is subjected to a state of tension, such that it is tightly wrapped around the drive roller, the ribbon reel is rotated by the cable as the type carrier carriage moves.
In the circumstances, by utilizing control elements located in the stationary part of the printing machine, the cable tension can be relaxed during the movement of the type carrier carriage to a return or row starting position, thus eliminating the drive movement to the ribbon reel. When a ribbon of finite length is used the two ribbon reels around which the ribbon is wound may be driven by different cables, which may be respectively alternately subjected to a condition of tension and a relaxed condition to thereby reverse the direction of movement of the ribbon. The corresponding control criterion for reversing the direction of movement of the ribbon may involve the tension of the ribbon on the type carrier carriage and can be transmitted in previously known arrangements by means of suitable electric circuitry to a control mechanism located on the stationary portion of the printing machine.
Preferably the diameter of the drive roller which rotates the ribbon reel is approximately three times the core diameter of the ribbon reel. Thus, assuming a character feed step of one-tenth inch the ribbon is in each case advanced by at least the amount of the character line thickness of approximately 0.8 mm per character print-out.
In one embodiment of the invention the cable is selectively tensioned by means of a spring element, and is returned to a relaxed condition by means of adjustable control elements which effectively counteract the biasing force of the spring element. Thus as the type carrier carriage is disposed in a starting position at the beginning of a row of characters to be printed, the cable, under the influence of the bias of the spring element, firmly grips the drive rollers to rotate the ribbon reels as the type carrier carriage moves across the row. On the other hand, after the completion of a row of printed characters, and as the type carrier carriage is moving back to a starting position to commence the printing of the next row, the biasing effect of the spring element is eliminated, resulting in a slackening of the cable loop around the drive rollers whereby the ribbon reels are not subjected to a turning force. Suitable means such as an electro-magnet may be utilized to counteract or offset the biasing effect of the spring element as the type carrier carriage is returned to a starting position.
If a ribbon of finite length is wound back and forth between two ribbon reels, a common electro-magnet may be utilized in association with a spring element which, by virtue of a single two-armed pivot lever, selectively maintains one of a pair of cables relaxed and the other in a condition of tension. The pivot lever for the two cables can conveniently comprise a two-armed hinged armature of an electro-magnet. In this arrangement, as electro-magnet is de-energized during the return movement of the type carrier carriage, one of the two cables is relieved while the second cable is subjected to spring tension. Since the return movement of the type carrier carriage itself counteracts the spring force, the cable which is tensioned by the spring force is also somewhat slackened such that the drive connection between the cables and the ribbon reels are eliminated. Thus the ribbon remains stationary with respect to the ribbon reels and the type carrier carriage as the carriage returns to its starting position upon completion of a printing cycle.
While the return movement of the type carrier carriage may be sufficient in and of itself to satisfactorily overcome or counteract the bias of the spring element during a return movement of the carriage, any tendency which the cables may have to move the ribbon may be eliminated by utilizing idler mechanisms between the ribbon reels and the drive rollers about which the cables are looped.
By increasing the number of loop windings of the cable around the drive rollers the tension forces transferred to the rollers may be increased. Further, the degree of adhesion or friction between the drive rollers and the cables can be influenced by a suitable selection of the materials employed. In a preferred embodiment the cable is made of steel and the drive rollers are provided with steel treads.
Many other features, advantages and additional objects of the present invention will become manifest to those versed in the art upon making reference to the detailed description which follows and the accompanying sheets of drawings, in which preferred structural embodiments incorporating the principles of the present invention are shown by way of illustrative example only.